The last decade has seen radical changes in the selection and use of refrigerants, mainly in response to the environmental issues of ‘holes in the ozone layer’ and ‘global warming or greenhouse effect’.

Previously there had not been much discussion about the choice of refrigerant, as the majority of applications could be met by the well known and well-tested fluids, R11, R12, R22, R502 and ammonia (R717).

The only one of these fluids to be considered environmentally friendly today is ammonia, but it is not readily suited to commercial or air-conditioning refrigeration applications because of its toxicity, flammability and attack by copper.

It will be useful to remind ourselves of the requirements for a fluid used as a refrigerant.

No single fluid has all these properties, and meets the new environmental requirements, but this chapter will show the developments that are taking place in influencing the selection and choice of a refrigerant.